Field of the Invention
The present invention relates to a sheet processing apparatus configured to perform folding processing on a sheet or a bundle of sheets delivered from an image forming apparatus, and further relates to an image forming system including the sheet processing apparatus.
Description of the Related Art
Hitherto, there has been provided a sheet processing apparatus configured to perform folding processing on a bundle of sheets to form a booklet, as post-processing for a sheet delivered from image forming apparatus such as a copying machine, a printer, a facsimile, and a multifunctional peripheral of those devices. For example, there has been known a sheet processing apparatus configured to align a plurality of sheets sequentially conveyed from an image forming apparatus to form a bundle of sheets, perform binding processing with a stapling device, fold the bundle of sheets at a bound portion thereof and thrust the bundle of sheets to a press-contact portion of a folding roller pair with a thrust plate, and fold the bundle of sheets in half while conveying the bundle of sheets with the folding roller pair (Japanese Patent Application Laid-Open No. 2009-126687).
In the sheet processing apparatus, the folding roller pair is disposed on one side across a sheet stack guide as a stacking tray for sheets to be subjected to the binding processing and the folding processing, from the thrust plate which is disposed on the other side opposite to the folding roller pair. In order to prevent sheet jamming which may be caused by a contact of a sheet to be conveyed to the sheet stack guide with the folding roller pair, an opening and closing shutter is disposed as a regulating member between the folding roller pair and the sheet stack guide.
In the conventional apparatus described in Japanese Patent Application Laid-Open No. 2009-126687, the opening and closing shutter is disposed so as to be raised and lowered by a motor along a sheet carry-in direction of the sheet stack guide. When a sheet is to be conveyed to the sheet stack guide, the opening and closing shutter is raised to block a thrusting path of the thrust plate which advances toward the press-contact portion of the folding roller pair serving as a rotary member pair. When the folding processing is to be performed, the opening and closing shutter is lowered to open the thrusting path. Raising and lowering of the opening and closing shutter are performed by controlling driving of the motor.
However, the opening and closing shutter is raised and lowered for each of the folding processing operation, and hence it is not easy to always stably stop the opening and closing shutter at a predetermined position with respect to the folding roller pair when the thrusting path is to be blocked. In particular, when there is variation in position of the opening and closing shutter at the time of conveying a sheet, a leading edge of the sheet to be conveyed may be caught by outer circumferential surfaces of the folding roller pair or by the opening and closing shutter. Thus, there is a concern of causing sheet jamming.